Refractory plate for a device for the insertion and/or removal of a nozzle for a casting installation combined with a sliding plate flow-control device

ABSTRACT

The invention relates to a refractory plate for a device for the insertion and/or removal of a nozzle for a casting installation combined with a sliding plate flow-control device comprising a) a first surface ( 1 ) provided with an orifice ( 2 ) defining the entry of a casting channel ( 3 ) through the plate and able to form a sealing surface, at least around the orifice ( 2 ), with a face matching the face of a mobile plate of the flow-control device; b) a second surface ( 4 ) adapted to rest in housing of the device and provided with a plane protuberance ( 5 ) circumscribing the casting channel ( 3 ) and extending through the bottom wall of the housing, and c) a third surface ( 6 ) defined by the plane surface of the protuberance ( 5 ) provided with an orifice ( 7 ), with a matching face of a refractory tube in casting position, and to act as guiding surface for the refractory tube from an introduction position to a casting position, and being shaped so that the portion of the third surface ( 6 ) in contact with the matching surface of the refractory tube increases as the tube progresses from the introduction position to the casting position. With this plate, an optimal compromise between the necessity to support at most the lower part of the plate while maximizing the lower surface available for guiding the tube from its introduction position to the casting position.

The present invention relates to a refractory plate for a device for theinsertion and/or removal of a nozzle for a casting installation combinedwith a sliding plate flow-control device.

The casting of a melt is generally carried out with an installationcomprising several refractory elements forming a casting channel betweentwo consecutive metallurgical containers. These elements fulfilldifferent functions which are the transfer of the melt, the protectionof the melt against cooling and the chemical attacks of the surroundingatmosphere and, optionally, the control of the melt casting flow. Thus,in the continuous casting, the melt contained in a casting ladle ispoured through a discharge orifice arranged in the bottom wall of theladle and prolonged by a nozzle extending through the bottom wall. Underthe bottom wall, there is generally a device for the flow-control of theliquid metal stream, the device being constituted from refractory platesprovided each with a casting orifice which can be aligned or shifted onewith respect to the other by the relative displacement of the plates soas to modify the cross-sectional flow area defined by the superpositionof the pouring orifices. The melt exits from the flow-control deviceinto a nozzle, having generally a small length and called collectornozzle. The most often, a casting tube intended for shrouding the streamdischarged from the collector nozzle during its way to a tundish isprovided. Conventionally, this shroud is fitted on the downstream end ofthe collector nozzle. From the U.S. Pat. No. 5,695,674, a castinginstallation wherein the collector nozzle and the shrouding nozzle forman assembly introduced into the casting position by sliding intoguide-rails is however also known. The International patent applicationWO-A1-9920420 discloses such a shrouding tube.

The metal poured through the shrouding tube into the tundish is thendirected towards one or more pouring orifices arranged in the bottomwall of the tundish. This orifice is prolonged by a nozzle which can rundirectly into the ingot-mold. In this case, the flow-control of the meltpoured from the tundish is performed with a stopper system which canclose the pouring orifice arranged in the bottom wall. In a variant, thenozzle can be formed of several adjacent elements, in particular, aninner nozzle ending upstreamly with the pouring orifice arranged in thebottom wall and downstreamly with an end formed as a plane surface and asubentry nozzle ending upstreamly with a plane surface matching theplane surface of the inner nozzle. Such an installation allows thereplacement with an appropriate device (such as described for example inthe patent EP-A1-192,019) of the subentry nozzle without having tointerrupt the casting. In this case also, the flow-control of the meltpoured from the tundish Is performed with a stopper system which canclose the pouring orifice arranged in the bottom wall. Another variantwherein a flow-control device with plates working according to the sameprinciple as the flow-control device above described in the context ofthe casting ladle is inserted between the inner nozzle and the subentrynozzle is also known. The patent EP-B1-441,927 discloses such a kind ofinstallation.

The present invention relates more particularly to an installationcomprising a device for the insertion and/or removal of a nozzle for acasting Installation combined with a sliding plate flow-control device.

The possibility to insert and/or to exchange a nozzle during the castingwithout having to interrupt it has been mentioned hereabove. The pouringnozzle intended to lead the melt from a metallurgical container towardsanother one are indeed wear parts which are strongly mechanically,chemically and thermally stressed to an extent that their service lifecan limit the casting time. In this context, there are many problemsthat the invention propose to solve with the plate according to thepresent invention.

Indeed, the lower plate of the sliding plates flow-control device isalso the stationary plate of the device for the insertion and/or removalof a nozzle for a casting installation combined with a sliding plateflow-control device against which the nozzle is brought from aninsertion position towards a casting position by the device for theinsertion and/or removal. These two functions impose hardly reconcilablerequirements:

-   -   the lower plate of the sliding flow-control device must rest in        a housing supporting it at most so as to provide a perfect seal        between its upper face and the matching surface of the mobile        plate of the flow-control device, but, at the same time,    -   its lower face must permit to guide the nozzle during its        displacement from the introduction position towards its casting        position.

If the plate is not enough supported into its housing, the plate isindeed not homogeneously supported. In particular, the pressure is notuniformly distributed around the pouring orifice of the plate and anincident called “finning” consisting in the formation of a thin strip offrozen metal between the stationary plate and the mobile plate, can takeplace. If this incident occurs repeatedly, the frozen metal strip actsas a wedge and push apart the two plates. It can even end with aninfiltration of molten metal which cause the immediate termination ofthe casting operations.

If the guiding surface is not sufficient to permit a correct guiding ofthe nozzle from the introduction position towards the casting position,the risk to have this casting nozzle in an incorrect position isimportant with all the adverse consequences that one can imagine.

Moreover, for economical reasons, it is important that the refractoryplates have as low as possible dimensions, in, in particular as to itsthickness. However, the casting channel extending through the lower pateof the sliding plate flow-control device is subjected to a very strongerosion due to the turbulent and asymmetrical molten metal streampassing through it. In particular, it is essential to prevent the metalstream so deviated (unbalanced) to hit the casting channel wall in thevicinity of its exit orifice, otherwise, the risk to damage the sealformed by the contact with the adjacent refractory element around theorifice of the casting channel would be great.

The inventors have thus seek to solve these problems and have come tothe idea of providing the plate in question with a protuberance. Evenso, its shape still had to be optimized so as to solve the abovementioned problems.

In order to permit a better understanding of the invention, it will nowbe described on the basis of the illustrative figures, which however donot limit it in any way. On these figures, top views of two differentrefractory plates according to the invention have been depicted on FIGS.1 and 1 a. FIGS. 2 and 2 a show to cross-sectional views according tothe line A-A respectively of FIGS. 1 and 1 a. FIG. 3 shows across-sectional view according to the line B-B of FIG. 1. FIGS. 4 and 4a show perspective views from the lower face of the plates respectivelyof FIGS. 1 and 1 a.

According to the invention, the refractory plate for a device for theinsertion and/or removal of a nozzle for a casting installation combinedwith a sliding plate flow-control device comprises the followingelements:

-   a) a first surface (1) provided with an orifice (2) defining the    entry of a casting channel (3) through the plate and able to form a    sealing surface, at least around the orifice (2), with a face    matching the face of a mobile plate of the flow-control device;-   b) a second surface (4) adapted to rest in housing of the device and    provided with a plane protuberance (5) circumscribing the casting    channel (3) and extending through the bottom wall of the housing,    and-   c) a third surface (6) defined by the plane surface of the    protuberance (5) provided with an orifice (7) defining the exit of    the casting channel (3) through the plate. It is essential that the    surface (6) be adapted    -   to form a sealing surface, at least around the orifice (7), with        a matching face of a refractory nozzle in casting position, and    -   to act as guiding surface for the refractory tube from an        introduction position to a casting position, and being shaped so        that the portion of the third surface (6) of the plate in        contact with the matching surface of the refractory tube        increases as the tube progresses from the introduction position        to the casting position.

With this plate, an optimal compromise between the necessity to supportat most the lower part of the plate while maximizing the lower surfaceavailable for guiding the tube from its introduction position to thecasting position.

The preferred shape for the protuberance is a tip shape, the tip (8)being directed towards the introduction position of the refractory tube.Henceforth, the initial efforts required to move the tube from itsintroduction position are quite low and increase progressively as thetube moves closer to its casting position. In case the tube is notperfectly aligned in the nozzle insertion and/or removal device, thisparticular shape allows an adjustment of the tube during its progressionin the device.

Particularly suitable shape are the oval, triangle, or egg shapes. Theegg shape (see on the FIGS. 1, 1 a, 4 and 4 a) permitting to avoid sharpangles and maximizing the above described effect is particularlypreferred.

The presence of a chamfer at the end of the tip (8) strengthen even morethis advantageous effect.

Alternatively, it Is also possible to have a chamfer on the opposite endof the tip (8). This is particularly advantageous when it is necessaryto bring to the casting position, or to any other appropriate position,another tube or any other refractory element which has to be Introducedfrom a direction opposite to the tube introduction direction. Forexample, this can be a collector nozzle which would be parked in awaiting position on the other side of the device.

The plate according to the invention can or not be provided with ametallic envelope.

If it is desired to protect the metal stream from the ambient atmospherelikely to contaminate the molten metal stream by passing through theseal either around the entry orifice (2) between the surface (1) and thelower surface of the sliding plate flow-control device or around theexit orifice (7) of the surface (6) and the upper surface of the tube,it is also possible to provide means permitting the formation of aninert gas shrouding channel circumscribing the orifice to protect. Forexample, one can have an inert gas line (9) feeding a circular groove(10) circumscribing the exit orifice (7) in the third surface (6) asdepicted on the FIGS. 1 to 4. A groove similar of or any other kind canbe present around the orifice (2).

Eventually, according to another advantageous variant of the invention,a second passage (12) extending through the plate from an orifice (11)of the third surface (6) towards an orifice (13) of the first surface(1) is provided. Preferably, this second passage (12) will have smallerdimension than the casting channel (3) and will be localized far fromthe casting channel (3), for example close to the end of the tip (8).This embodiment is depicted on FIGS. 1 a, 2 a and 4 a.

In case it is not possible to start naturally the casting sequence, justby opening the flow-control device, it is then possible to bring thissecond passage in register with the casting channel of the mobile plateand to introduce, through the passage (12) and the orifices of thedownstream refractory elements a lancing device which will allow, forexample by oxygen lancing to free the casting channel from anyobstruction. In this case, it can be useful to position a collectornozzle (11) under the orifice (11) or to have a refractory provided withmeans allowing the access to the casting channel passing through therefractory plates.

1-9. (canceled)
 10. Refractory plate for a device for the insertionand/or removal of a nozzle for a casting installation combined with asliding plate flow-control device comprising a) a first surface providedwith an orifice defining the entry of a casting channel through theplate and able to form a sealing surface, at least around the orifice,with a face matching the face of a sliding plate of the flow-controldevice; b) a second surface adapted to rest in housing of the device andprovided with a plane protuberance circumscribing the casting channeland extending through the bottom wall of the housing, and c) atip-shaped third surface defined by the plane surface of theprotuberance provided with an orifice defining the exit of the castingchannel through the plate, the surface being adapted (i) to form asealing surface, at least around the orifice, with a matching face of arefractory nozzle in casting position, and (ii) to act as guidingsurface for the refractory nozzle from an introduction position to acasting position, the tip being directed towards the introductionposition of the refractory nozzle.
 11. Refractory plate according toclaim 10, wherein the third surface is provided with a chamfer at theend of the tip.
 12. Refractory plate according to claim 10, wherein thethird surface is provided with a chamfer on the side opposite to the endof the tip.
 13. Refractory plate according to claim 10, wherein thethird surface is oval-shaped.
 14. Refractory plate according to claim10, wherein the third surface is triangle shaped.
 15. Refractory plateaccording to claim 10, wherein the third surface is egg-shaped. 16.Refractory plate according to claim 10, wherein it is provided withinert gas supplying means.
 17. Refractory plate according to claim 16,wherein the inert gas supplying means comprises a gas feeding line and acircular groove circumscribing the exit orifice of the casting channelin the third surface.
 18. Refractory plate according to claim 10,wherein the third surface is provided with a second orifice close to theend of the tip.